The death toll from the worst Ebola outbreak in history has jumped by almost 200 in a single day to at least 2,296 and is already likely to be higher than that, the World Health Organization said on Tuesday.

The WHO said it had recorded 4,293 cases in five West African countries as of Sept. 6, a day after its previous update.

But it still did not have new figures for Liberia, the worst-affected country, suggesting the true toll is already much higher. The WHO has said it expects thousands of new cases in Liberia in the next three weeks.

Liberian President Ellen Johnson Sirleaf said on Tuesday she expects the Ebola crisis gripping her country to worsen in the coming weeks as health workers struggle with inadequate supplies, a lack of outside support and a population in fear.

(CNN) — The Bill and Melinda Gates Foundation announced Wednesday it will donate $50 million to help fight the Ebola outbreak in West Africa.

More than 2,200 people have died in Guinea, Liberia and Sierra Leone, where the outbreak has been concentrated. Cases have also been reported in nearby Nigeria and Senegal.

The foundation says the money will be used to enable international aid organizations and national governments “to purchase badly needed supplies and scale up emergency operations in affected countries.”

It will also “work with public and private sector partners to accelerate the development of therapies, vaccines, and diagnostics that could be effective in treating patients and preventing further transmission of the disease.”

The first human trial of an experimental Ebola vaccine began last week at the National Institutes of Health.

This is considered the deadliest Ebola outbreak in history. The World Health Organization said Monday the rapid spread of the virus in Liberia shows no sign of slowing.